Separate Collision Bounds
I'm not totally sure if what you are saying is possible. Someone else would have to comment on that.

However, I do know what I would do to fix it.


Create a new object for each section you would like. (Tip: perhapse you could use empties to avoid step 4)
Parent your new collision objects to the main object for which you are tracking collision.
Set up the scripts so that when one of these objects is hit, it sends a message to the parent object.
Set these collision objects to not be rendered and not affect physics simulations (gravity, collision, etc.)


I hope this method helps.

Thanks, Uncle Snail